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Ther e s a second problem wit h t he Web page show n in Figur e 11- 26 besides t he fact t hat t he t ext box ent ries ar e invalid. We ll highlight t his second issue in t he nex t sect ion when we refer back t o t he figure. Pr ogr a m m in g t h e Pa ge I sVa lid Pr ope r t y
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Validat or cont rols will pass a Web page t o t he browser if y ou set t he EnableClient Scr ipt pr opert y t o False, ev en if one or m ore cont rols on a page m ak e t he page invalid. The sam e act ion also t ak es place if t he client w or kst at ion
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disables client - side script ing or if t he client - side script ing capabilit y for a browser is incom pat ible w it h ECMAScr ipt 1.2, a subset of Microsoft JScr ipt . Alt hough t he validat or cont rols do operat e on a Web serv er when client - side v alidat ion doesn t t ake place, event procedur es for t he page also operat e. The operat ion of t hese ev ent procedures, such as for a pr ocedur e t o insert a new row in a t able, can ent er invalid dat a in a dat abase. Despit e t he issues highlight ed in t he pr eceding paragraph, using serv er- side validat ion is cleaner t han client - side validat ion because it doesn t depend on t he capabilit ies of a br owser ( or even w het her client - side script ing is disabled in a browser t hat has t he capabilit y ) . However, t o t ak e advant age of serv er- side validat ion, y ou need t he Web ser ver t o be able t o det ect whet her a page has valid cont r ols and t hen condit ionally ex ecut e dat a m anipulat ion or dat a access t asks based on t he validit y of t he cont rols.
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I f you use ser ver- side v alidat ion wit hout m aking dat a m anipulat ion t ask s, such as inser t s and updat es, condit ional on t he v alidit y of t he cont rols on a page, y ou r un t he r isk of ent er ing invalid dat a in your dat abase. When y ou com bine server- side validat ion wit h invalid dat a, a r elat ed pr oblem em erges. The error m essages for dat a will be one row out of sy nchr ony wit h t he inv alid dat a. As a r esult , error m essages will appear on pages wit h v alid dat a, and pages wit h invalid dat a will appear wit hout err or m essages.
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You can use t he I sValid propert y for a Page obj ect t o det ect on a Web ser ver whet her t he page t o w hich a Page obj ect point s has any invalid cont r ols before com m it t ing an insert or an updat e t o a dat abase. I f any cont rols are inv alid, you can bypass t he code t o insert a new r ow or updat e an ex ist ing r ow w it h t he dat a from t he invalid cont r ols. WebForm 1.aspx in t he I sValidSam ple pr oj ect dem onst rat es t he synt ax for using t he I sValid propert y for a Page obj ect . The I sValidSam ple pr oj ect is ident ical t o t he Validat orUI Sam ple pr oj ect in t he preceding sect ion except for t he follow ing Visual Basic code t o im plem ent t he cm dI nsert _Click ev ent procedur e. Bot h proj ect s assign False t o t he EnableClient Scr ipt pr opert y for all validat or cont rols, w hich forces serv er- side validat ion. The Validat or UI Sam ple pr oj ect uses t he logic from t he Dat a Manipulat ion from ASP. NET sect ion t o im plem ent t he cm dI nsert _Click ev ent procedur e. The I sValidSam ple proj ect insert s a new row w it h t he following adapt at ion of t he code from t he Validat or UI Sam ple pr oj ect . Not ice t he use of t he Me nam e t o point t o t he cur rent page. I f any cont rol on t he page is invalid, t he I sValid pr opert y is False, and t he procedur e doesn t invoke t he Updat e m et hod. I nst ead, t he page ret ur ns t o t he browser wit h t he err or m essage or m essages show ing. I f t he page s I sValid propert y is True, t he procedure execut es t he Updat e m et hod and t he browser shows t he last row in t he local ASPNETShippers Dat aTable, which cont ains t he m ost r ecent ly insert ed row. Private Sub cmdInsert_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles cmdInsert.Click Add text box values to new row in dataset Shippers table. Dim newRow As DataRow = das1.Tables( ASPNETShippers ).NewRow() newRow( CompanyName ) = TextBox2.Text newRow( Phone ) = TextBox3.Text das1.Tables( ASPNETShippers ).Rows.Add(newRow)
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Update method synchronizes inserted local row with its copy in northwind and returns the identity column value added by the northwind database. If Me.IsValid Then dap1.Update(das1, ASPNETShippers ) Move to last row and populate text boxes Session( MyRowID ) = _ das1.Tables( ASPNETShippers ).Rows.Count - 1 MoveToRow() End If End Sub Figur es 11- 27 and 11- 28 show t he WebForm 1.aspx page from t he I sValidSam ple proj ect in operat ion. Figur e 11- 27 shows t he r esult fr om an at t em pt t o insert a new row wit h an invalid Phone field value. ( I t ends wit h t he let t er r inst ead of a num ber.) Not ice t hat t he er ror m essage at t he bot t om of t he screen and t he ast erisk highlight t he problem and inst r uct t he user w hat t o do ( fix t he er ror and reinsert ) . Also, not ice t hat t he ShipperI D t ext box is em pt y. This is because t he procedur e didn t at t em pt t o execut e t he I nsert st at em ent w it h invalid dat a according t o t he Web page validat or cont r ols. Figure 11- 28 shows t he Web page ret ur ned by t he Web serv er aft er t he user changes t he last charact er in t he Phone t ext box fr om r t o 4. Not ice t hat t his v ersion includes a ShipperI D value, indicat ing t hat t he Web serv er subm it t ed t he new r ow t o t he SQL Serv er inst ance and receiv ed a new colum n value as an out put param et er value fr om t he st or ed procedur e t hat perform ed t he insert . Figu r e 1 1 - 2 7 . W e bFor m 1 .a sp x from t h e I sVa lidSa m ple pr oj e ct w it h an in va lid valu e in t h e Ph on e t ex t box .
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Figu r e 1 1 - 2 8 . W eb For m 1 .a spx fr om t h e I sVa lid Sa m p le p roj ect a f t er it s fix .
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Now s a good t im e t o focus on t he second problem w it h Figur e 11- 26. Not ice t hat it com m it t ed t he row w it h invalid Com panyNam e and Phone colum n v alues t o t he ASPNETShippers t able. The reason you can t ell is t hat t he Web page shows a ShipperI D value, which SQL Ser ver assigns only aft er it insert s a record int o a t able. Unless t he user delet es t he fault y row, t he error m essages can com e out of sync wit h t he dat a showing on a Web page. The user can get r id of t he fault y row by clicking t he Delet e but t on on t he Web page. However, t his act ion r equir es t he user t o st art ent ering t he new r ow ov er again fr om scrat ch. I f t he Web page had a Modify but t on, which I rem ov ed t o sim plify t he sam ple, t he user could use t hat but t on t o fix t he page. Howev er, t he r eal problem w it h WebForm 1.aspx in t he Validat orUI Sam ple pr oj ect is t hat t he Web page insert s t he new row uncondit ionally ( w het her or not t he dat a on t he page is invalid) . I t is t his problem t hat t he I sValidSam ple proj ect corr ect s.
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